Haggle is a networking architecture for data-centric opportunistic communication. In laymen's terms, it means that Haggle allows mobile phones to exchange items of data directly between themselves whenever they happen to come in close range. The data to exchange is based on the interests that users express in data. Contact opportunities are unpredictable and make communication inherently asynchronous, rather than synchronous as is the case with the Internet architecture. Haggle supports both Bluetooth and WiFi connectivity.

Haggle has a simple publish/subscribe API that makes it easy to write applications. An application could, for example, exchange pictures or songs between mobile phones based on the users' interests.

PhotoShare is an example Haggle application created to illustrate how easy it is to write Haggle applications using the APIs. PhotoShare exists in two versions: one for Windows mobile and one for Android.

PhotoShare allows a user with a mobile phone to easily share pictures taken with the phone's camera. When taking a picture, the user can annotate it with any number of keywords that will be added to the picture's metadata. The picture is then published in the Haggle network and users that have interests matching the metadata will receive it. The more interests that match a picture's metadata, the higher the likelihood is that the user will receive the picture.

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